Memory system having incorrupted strobe signals

ABSTRACT

A memory system circuit and method therefor are disclosed. The circuit is adapted to detect a transition in a data timing signal from an indeterminate logic level to a selected one of a high logic level and a low logic level. The circuit includes a comparator having a first input, a second input and an output. The first and second inputs receive the data timing signal and a reference voltage respectively. The output changes logic levels in response to a change in polarity of a voltage difference between the voltage of the timing signal and the reference voltage. The reference voltage is sufficiently closer to the selected one of the logic levels as compared to the other of the logic levels so as to at least substantially prevent potential false positive detections.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/780,231 filed on Jul. 19, 2007 which is incorporated herein byreference in its entirety.

BACKGROUND OF THE DISCLOSURE

Microelectronics circuits include a variety of different circuitcomponents, and one type of circuit component that is often found inthese circuits is a comparator. The comparator is a circuit element withtwo inputs labeled positive and negative and one output. The output goeseither high or low depending upon which input is greater.

As will be appreciated by those skilled in the art, the signals beingreceived by comparators are often noisy. When the input voltage of thereceived signal is close to the threshold voltage of the comparator, onepotential problem is that a small amount of noise can make the voltageat the input rapidly fluctuate to values just above or just below thethreshold voltage for the comparator. This can cause output “glitches”that may cause instability in the larger circuit, perhaps a controlcircuit, for example, that is impacted by the output of the comparator.

Existing solutions outside of the field of memory systems includesolutions that employ a Schmidt Trigger. In this regard, one skilled inthe art will appreciate that a Schmidt Trigger makes use of feedback, sothat the current output state essentially “reinforces” the input value.For instance, if the output state is currently logic “high” (logic ‘1’)there will not be an output transition to logic “low” (logic ‘0’) unlessthe input voltage drops substantially below a low threshold voltage.Conversely, if the output state is currently logic ‘0’, there will notbe an output transition to logic ‘1’ unless the input voltage risessubstantially above a high threshold voltage. The difference in the twothreshold voltages can be referred to as the hysteresis voltage.

A problem with Schmidt Triggers is that they are not designed to work inmemory systems, and therefore the principles of hysteresis haveapparently not previously been applied in the context of providingincorrupted strobe signals within a memory system.

SUMMARY

It is an object of the invention to provide an improved memory system.

According to one aspect of the invention, there is provided a method forpreamble detection within a microelectronics system. The method includesthe step of receiving a clock signal of the type in which a series ofregular pulses in voltage level of the clock signal are preceded by apreamble period having a beginning and an end. A transition in the clocksignal from an indeterminate logic level to a selected one of a highlogic level and a low logic level occurs at the beginning of thepreamble period. The method also includes the step of receiving acomplement of the clock signal. A transition in the complement of theclock signal from the indeterminate logic level to the other of thelogic levels occurs at the beginning of the preamble period. The methodalso includes the step of generating indication that the beginning ofthe preamble period has occurred by: i) detecting the transition in theclock signal based on when the voltage level of the clock signal crossesthrough a first threshold of a voltage range; and ii) detecting thetransition in the complement of the clock signal based on when thevoltage level of the complement of the clock signal crosses through asecond threshold of the voltage range.

According to another aspect of the invention, there is provided anindication circuit in a memory system within which a clock signal and acomplement of the clock signal are generated. The clock signal is of thetype in which a series of regular pulses in voltage level of the clocksignal are preceded by a preamble period having a beginning and an end.A transition in the clock signal from an indeterminate logic level to aselected one of a high logic level and a low logic level occurs at thebeginning of the preamble period. A transition in the complement of theclock signal from the indeterminate logic level to the other of thelogic levels occurs at the beginning of the preamble period. The circuitincludes a first comparator having first and second inputs. The firstcomparator is adapted to detect, when the clock signal and a firstreference voltage are received at the first and second inputs of thefirst comparator respectively, a change in polarity of a voltagedifference between the voltage of the clock signal and the firstreference voltage. A second comparator has first and second inputs. Thesecond comparator is adapted to detect, when the complement of the clocksignal and a second reference voltage are received at the first andsecond inputs of the second comparator respectively, a change inpolarity of a voltage difference between the voltage of the complementof the clock signal and the second reference voltage. The circuit alsoincludes logic circuitry for generating indication, by way of an outputsignal of the logic circuitry transitioning to an active logic level,that the beginning of the preamble period has occurred. The indicationis generated when the transitions in the clock signals are detected.

According to yet another aspect of the invention, there is provided amemory controller circuit for detecting a transition in a data timingsignal from an indeterminate logic level to a selected one of a highlogic level and a low logic level. The circuit includes a comparatorhaving a first input, a second input and an output. The first and secondinputs receive the data timing signal and a reference voltagerespectively. A signal from the output changes logic levels in responseto a change in polarity of a voltage difference between the voltage ofthe data timing signal and the reference voltage. The reference voltageis sufficiently close to the one of the logic levels, whereby at leastsubstantial prevention of potential false positive detections isachieved.

Thus, improved signal transition detection circuits for memory systemshave been provided.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made, by way of example, to the accompanyingdrawings:

FIG. 1 is a block diagram of a synchronous dynamic random access memorydevice that includes a data strobe clock (DQS) enable circuit inaccordance with an example embodiment;

FIG. 2 is a timing diagram illustrating a DQS over a number of timeperiods;

FIG. 3 is a circuit schematic representation of a number of memorycontroller circuits, including a DQS transition detection circuit inaccordance with an example embodiment;

FIG. 4 is a timing diagram illustrating the operation of a preambleindication circuit within the DQS enable circuit of FIG. 3;

FIG. 5 is a circuit schematic representation of a DQS transitiondetection circuit in accordance with an alternative example embodiment;and

FIG. 6 is a timing diagram illustrating the operation of the DQStransition detection circuit of FIG. 5.

Similar or the same reference numerals may have been used in differentfigures to denote similar components.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Referring now to the drawings, FIG. 1 is a block diagram of a

Synchronous Dynamic Random Access Memory (SDRAM) device 10 that includesa memory controller 20 and a Double Data Rate Synchronous Dynamic RandomAccess Memory (DDR SDRAM) 22. In terms of the DDR SDRAM 22, thoseskilled in the art will appreciate that a characteristic of it isoperation at twice the speed relative to the clock, because the latchingor accessing of data occurs at both rising and falling edges of DQS. Theillustrated DDR SDRAM 22 is connected to the memory controller 20through connections including: a unidirectional bus 24 used to sendaddresses, commands and clocks from the memory controller 20 to the DDRSDRAM 22; a bi-directional bus 26 for writing data (DQ) to the DDR SDRAM22 and reading DQ from the memory; and bi-directional connections 28 and29 for carrying data strobe clock (DQS) and the complement of DQSrespectively.

As will be appreciated by those skilled in the art, DQS is a specialclock signal, which is, in turn, a type of data timing signal. Also, DQSis employed in read and write operations. Partly in keeping with atypical clock signal, DQS is a sequence of electronic pulses for aportion of a read or write operation; however at other times when a reador write operation is not occurring, DQS is in high-impedance and at anindeterminate logic level (in between logic ‘1’ and logic ‘0’). In awrite operation, DQS is generated synchronously with the write data bythe memory controller 20, and also DQ for the write operation will beinputted, in some examples, to a suitable buffer in anticipation ofbeing stored in a manner understood by those skilled in the art, inparticular, in a data latch with the rising and falling edges of DQS. Ina read operation, DQS and read data from the DDR SDRAM 22 are generatedsynchronously by the memory and, as will be appreciated by those skilledin the art, DQ for the read operation will, in some examples, beinputted to a suitable buffer in anticipation of being stored in a datalatch with the rising and falling edges of DQS.

Before continuing with the present description of the SDRAM device 10,it should be noted that the memory controller 20 and the DDR SDRAM 22comprise many individual circuits and components for carrying out theirrespective functions. Because one skilled in the art need not have anunderstanding of how to design or modify all components of the memorycontroller 20 and the DDR SDRAM 22 in order to obtain the benefits ofthe teachings disclosed herein, it will be understood that only relevantcircuits and components are shown and described in detail.

With reference now to the memory controller 20 of FIG. 1, this will, insome examples, be an Application-Specific Integrated Circuit (ASIC). Thememory controller 20 operates a main clock. Also, the memory controller20 has, within a PHY (Physical Interface) 302, a DQS enable circuit 32that generates a gated DQS from the incoming DQS signal 28. The DQSenable circuit 32 will be further described later in connection with thedescription for a more detailed diagram.

Reference will now be made to FIG. 2. FIG. 2 illustrates signalstransitions for DQS when DQ is being captured in response totransmission of data from the DDR SDRAM 22. In addition to DQS,illustrated complement of DQS (DQS#) conveniently allows rising edges tobe provided to rising-edge triggered circuitry at instance in time whenfalling edges of DQS occur. Also, in some alternative examples, otherDQS-related signals (having waveforms differing from the illustratedwaveforms) could be generated in connection with a read command. Forexample, signals similar to illustrated DQS and DQS#, but with dutycycles significantly less than 50%, could be generated. Also, it will beunderstood that the term “complement” as it is used herein refers to apractical but not mathematical complement. For example, DQS and DQS# arenormally shifted apart some number of degrees off of the theoreticalamount of 180°.

For the purposes of the present discussion, it is fitting to divide theactivity in the DQS waveform into five periods of time. During a firstperiod of time, T1, DQS is in high-impedance. The next period is thepreamble period labeled in FIG. 2 as T2. This is typically a short setupperiod such as, for example, slightly less than one clock cycle, so asto permit DQ to be properly read. After T2 is a period T3, during whichtime DQ is read on edges of DQS (both rising and falling in theillustrated example). Ideally each of these edges will be aligned asclose as possible to a center of one of the data eyes of the data D0,D1, D2 and D3. As will be appreciated by those skilled in the art, aDelay Locked Loop (DLL) can be used to produce the phase shift of 90° ofDQS so that its edges will be properly aligned.

After T3 is the postamble period labeled in FIG. 2 as T4. Like T2, T4 istypically a short period (for example, slightly less than half a clockcycle) in order to provide for proper termination of the read operation.At the end of T4 there is a transition to a last illustrated period T5,and at this time DQS returns to the state it was in during T1 (i.e.high-impedance).

Thus, for periods of time before and after a read operation, DQS will bein high-impedance. As mentioned, the voltage assigned to the statecorresponding to high-impedance is roughly mid-level between logic ‘1’and logic ‘0’; however in actual implementations the voltage of DQS (andthe signal output of, for example, any comparator with mid-level voltagethreshold that buffers DQS) will fluctuate significant above and belowthe aforementioned mid-level voltage. Ensuring that the signalfluctuations do not cause anomalous behavior, such as, for example,erroneous reading of DQ when data is not available, is known to beproblematic.

Reference will now be made to FIGS. 1 and 3. FIG. 3 shows a circuitschematic representation of a DQS transition detection circuit inaccordance with an example embodiment. In the illustrated example, theDQS transition detection circuit is a DQS enable circuit 32. Also, theillustrated DQS transition detection circuit is situated within the PHY302 of the memory controller 20; however in some exampleimplementations, the DQS transition detection circuit might be situatedsomewhere else within the SDRAM device 10, such as within the DDR SDRAM22, for instance.

The PHY 302 is divided into a number of byte lanes in a manner known tothose skilled in the art. In particular, the illustrated PHY 302 isdivided into a byte lane 304 for I/Os, a byte lane 308 for InterfaceTiming Modules (ITMs), and a byte lane 312 for PLL(s). Conveniently, theillustrated byte lanes 304 and 308 are further divided into tileablecells (two of which are labeled 316 in FIG. 3). As will be appreciatedby those skilled in the art, the use of tileable cells facilitates theinterlacing of power and data signals having regard to inner and outerbond pads, and its use also provides for increased flexibility ascompared to if the byte lanes 304 and 308 were not further divided intotileable cells. The illustrated enable circuit 32 falls within sixtileable cells 316 (three cells of the byte lane 304 and three cells ofthe byte lane 308); however in alternative examples the DQS enablecircuit may fall within fewer or additional tileable cells. In at leastone example, it is convenient for the cells each separately containingcomparators 340 and 344 to be two instances of the same cell.

The illustrated enable circuit 32 includes a preamble indication circuit326, DQS enable logic circuitry 330, DQS disable First In First Out(FIFO) circuitry 332, multiplexing circuitry 334, multiplexing circuitry338, and the comparators 340 and 344. Input signals to the enablecircuit 32 include a DQS signal, a DQS# signal, a write_data signal, awrite_enable signal, and a system clock. Output signals from the enablecircuit 32 include an output signal of the multiplexing circuitry 334,and an output signal of the multiplexing circuitry 338.

Reference will now be made to the preamble indication circuit 326. Theindication circuit 326 includes comparators 350 and 354 and an AND logicgate 356 (with inversion at one of the gate inputs). The non-invertingand inverting inputs of the comparator 350 are electrically connectedto, respectively, DQS and a lower threshold V_(IL) of a voltage range.The non-inverting and inverting inputs of the comparator 354 areelectrically connected to, respectively, DQS# and an upper thresholdV_(IH) of the V_(IL)−V_(IH) voltage range. The output of the comparator350 is electrically connected to the input of the AND logic gate 356with preceding inversion. The output of the comparator 354 iselectrically connected to the other input of the AND logic gate 356. Theoutput of the AND logic gate 356 is electrically connected to the enablelogic circuitry 330.

The operation of the preamble indication circuit 326 during the DQSpreamble period (period T2 in FIG. 2) will now be explained withreference to FIGS. 3 and 4. FIG. 4 is a timing diagram showing thefollowing: DQS and DQS# (noisy in the illustrated example), DL (outputsignal of the comparator 350), DH (output signal of the comparator 354),and PI (output of the AND logic gate 356).

Now with reference to time t₁, which corresponds to a transition momentin time from the high-impedance period to the preamble period, it willbe seen that the voltage of DQS begins falling towards logic low, andthe voltage of DQS# begins rising towards logic high. As the voltage ofDQS begins falling towards logic low, DQS subsequently crosses throughvoltage V_(IL) (at time t₂ in the illustrated example). Thus the DQStransition is detected, and in response output signal DL of thecomparator 350 changes from logic high to logic low as indicated bytransition arrow 402.

While the voltage of DQS begins falling towards logic low at time t₁,the voltage of DQS# begins rising towards logic high at this time. DQS#then crosses through voltage V_(IH) (at time t₂ in the illustratedexample). Thus the DQS# transition is detected, and in response outputsignal DH of the comparator 354 changes from logic low to logic high asindicated by transition arrow 406. Thus signals at logic levelsnecessary for producing logic high on output signal PI (output of theAND logic gate 356) are received at the inputs of the AND logic gate356. Namely, logic low is received at the input with precedinginversion, and logic high is received at the other input. At logic high,the output signal PI provides indication that the preamble period hasoccurred as explained below. (It will be understood that exampleembodiments are not limited to those specific examples where thepreamble indication is low-to-high logic level transition.)

In the illustrated example, the output signal PI is received by the DQSenable logic circuitry 330. Output 360 of the enable logic circuitry 330is electrically connected to the selection inputs of the multiplexingcircuitries 334 and 338, and thus a change in the output 360 on the nextclock edge, that is brought about by preamble indication received fromthe preamble indication circuit 326, results in differential DQS−DQS#signals from the comparators 340 and 344 being selectively passedthrough the multiplexing circuitries 334 and 338 respectively.

In addition to being controlled in part by the output of the preambleindication circuit 326, the enable logic circuitry 330 is, in at leastone example, also controlled in part by the output of the disable FIFOcircuitry 332, which is in turn controlled in part by input signals‘write_data’ and ‘write_enable’. ‘Write_data’ defines the write databit, and ‘write_enable’ causes the output buffer to be turned on whenthe signal is at an active logic level.

With respect to a first differential DQS signal passed through themultiplexing circuitry 334, delay circuit 364 (a DLL, for example) phaseshifts the first differential DQS for proper alignment with DQ. In theillustrated example, the delay circuit 364 includes a slave DLL. In thisregard, it will be understood that, for any slave DLL in a memorycontroller, there will exist a corresponding master DLL also within thatmemory controller. The master DLL derives a 0° clock which is phaselocked to the main clock, and also 90°, 180°, and 270° phases. The slaveDLL creates a constant 90° phase shift.

Phase shifted by the delay circuit 364, the first delayed differentialDQS is made available along an electrical path 366, with a driver 368facilitating this as understood by those skilled in the art. The clockinput of a latch 370 (a D flip-flop in the illustrated example) iselectrically connected to the path 366 to receive the delayeddifferential DQS signal.

With respect to a second differential DQS signal passed through themultiplexing circuitry 338, delay circuit 372 (a DLL, for example) phaseshifts the second differential DQS for proper alignment with DQ. Thesecond delayed differential DQS is then made available along anelectrical path 376, with a driver 378 facilitating this as understoodby those skilled in the art. The clock input of a latch 380 (a Dflip-flop in the illustrated example) is electrically connected to thepath 376 to receive the delayed differential DQS signal.

In the illustrated example, both the latches 380 and 370 receive DQ attheir respective inputs as facilitated by driver 384 in a mannerunderstood by those skilled in the art. Each next data of DQ is providedto a data capture FIFO in an alternating manner from either the latch370 or 380, depending on which latch has its clock input brought activeat that time.

FIG. 5 is a circuit schematic representation of a DQS transitiondetection circuit 530 in accordance with an alternative exampleembodiment. The illustrated circuit 530 is similar to a Schmidt Triggerwith respect to its precision hysteresis characteristics, but unlike aSchmidt Trigger, one skilled in the art should understand that thecircuit shown in FIG. 5 has precise trigger points for hysteresis.

The illustrated circuit 530 includes two comparators 532 and 536, an R-Slatch 540 and a number of inverters. In operation, the circuit 530corrects a signal VI (DQS signal) that is applied at inputs of thecomparators 532 and 536, outputting a corrected signal at circuit output544. It will be understood that the signal VI could be corrupted ordistorted to at least some degree. For example, the signal VI may benoisy. Also, one skilled in the art will appreciate that the illustratedR-S latch 540 is an enable latch (level triggered); however it should beunderstood that in a number of contemplated embodiments any suitablestorage circuitry that functions in a manner similar to an R-S latchcould be employed.

With respect to the comparators 532 and 536, in at least some examplesthese are specialized comparators designed to be used as chip inputbuffers. In the illustrated circuit 530, non-inverting input 548 of thecomparator 532 is coupled to the signal VI, and inverting input 552 iscoupled to a reference voltage VR1 (high threshold of a hysteresisvoltage). With respect to the comparator 536, inverting input 554 iscoupled to the signal VI and non-inverting input 558 is coupled to areference voltage VR0 (low threshold of the hysteresis voltage). Boththe illustrated comparators 532 and 536 are provided with voltagesources MVDD and MVDDQ, the voltage source MVDD being intermediate MVDDQand ground potential. In some examples, MVDDQ is the I/O signalingvoltage, which is a selected one of 2.5V, 1.8V and 1.5V, and MVDD is thechip core voltage, which is a selected one of 1.0V and 1.2V.

Output 560 of the comparator 532 is coupled to a SET input of the R-Slatch 540, which is input 562 of NAND gate 564 in the illustratedexample embodiment. With respect to output 568 of the other comparatorin the circuit 530, it is coupled to the input of inverter 572. Theoutput of the inverter 572 is coupled to a RESET input of the R-S latch540, which is input 576 of NAND gate 578 in the illustrated exampleembodiment. Two additional NAND gates within the R-S latch 540 arecross-coupled NAND gates 582 and 584. Output 586 of the NAND gate 564 iscoupled to input 588 of the NAND gate 582, while output 590 of the NANDgate 578 is coupled to input 592 of the NAND gate 584. The illustratedR-S latch 540 also includes inverters 594 and 596 coupled to the outputsof the NAND gates 582 and 584 respectively. These inverters help preventa glitch at the NAND gate outputs that might cause erroneous flipping.The inverters 594 and 596 also provide drive.

Still with reference to FIG. 5, as long as the signal VI applied at theinput 548 of the comparator 532 is above the high threshold referencevoltage VR1 applied at the input 552, the state at the output 560 willbe logic ‘1’. In the case however where the signal VI applied at theinput 548 of the comparator 532 falls below the high threshold referencevoltage VR1, the state at the output 560 will transition from logic ‘1’to logic ‘0’. As for the other comparator, as long as the signal VIapplied at the input 554 of the comparator 536 is below the lowthreshold reference voltage VR0 applied at the input 558, the state atthe output 568 will be logic ‘0’. In the case however where the signalVI applied at the input 554 of the comparator 536 rises above the lowthreshold reference voltage VR0, the state at the output 568 willtransition from logic ‘0’ to logic ‘1’.

Based on the above, whether the illustrated R-S latch 540 is ‘set’ or‘reset’ will depend upon where the voltage of the signal VI fallsrelative to the reference voltages VR1 and VR0. If the voltage of thesignal VI is above the reference voltage VR1, logic ‘1’ and logic ‘0’will be applied to the SET and RESET inputs respectively. As will beappreciated by those skilled in the art, this condition ‘sets’ the R-Slatch 540 (i.e. causes logic ‘1’ to appear at the output 544). If thevoltage of the signal VI is in between the reference voltage VR1 and thereference voltage VR0, logic ‘0’ will be applied to both the SET andRESET inputs. As will be appreciated by those skilled in the art, thiscondition is the ‘hold’ condition for the R-S latch 540 (i.e. the stateat the output 544 remains the same). Finally, if the voltage of thesignal VI is below the reference voltage VR0, logic ‘0’ and logic ‘1’will be applied to the SET and RESET inputs respectively. It will beunderstood that this condition ‘resets’ the R-S latch 540 (i.e. causeslogic ‘0’ to appear at the output 544). With respect to an ENABLE signalreceived at an input of each of the NAND gates 564 and 578, the R-Slatch 540 passes through latch inputs signals when this signal is logiclow, and holds state when the signal is logic high.

The operation of the DQS transition detection circuit 530 with a noisyDQS signal applied as VI at the non-inverting input terminals of thecomparators 532 and 536 will now be explained with reference to FIG. 6.As can be seen in the timing diagram, at instances in time such ast_(y), for example, the logic level at the SET input of the R-S latch540 goes to logic high when VI rises above the high threshold referencevoltage VR1. Additionally, at instances in time such as t_(x), forexample, the logic level at the RESET input of the R-S latch 540 goes tologic high when VI falls below the low threshold reference voltage VR0.

It will be seen that at times t_(u) and t_(v) VI momentarily jumps above(sinks below) the reference voltage causing a corresponding momentarylogic high-to-low transition in the signal at the RESET input (SETinput). These short lived transitions do not produce an output valuechange in the R-S latch 540. In particular, the momentary logichigh-to-low transition in the signal at the RESET input following thethreshold crossing at t_(u) does not result in a change in logic levelsof the illustrated output signal Q because, as will be appreciated bythose skilled in the art, logic low at both inputs of an R-S latch meansthat Q(t+Δ)=Q(t) (i.e. what is frequently referred to as the ‘hold’state). Similarly (and for essentially the same reason) the momentarylogic high-to-low transition in the signal at the SET input followingthe threshold crossing at t_(v) does not result in a change in logiclevels of the illustrated output signal Q.

With reference to both FIGS. 2 and 6, the output signal Q shouldgenerally be an incorrupted strobe signal in spite of noise in VI solong as: i) during periods T2, T3 and T4, the noisy DQS signal does notanomalously jump/sink through the entire hysteresis voltage range; andii) during the indeterminate periods (T1 and T5) the noisy DQS signalstays within the hysteresis voltage range. It is theorized that, incertain memory systems, the DQS transition detection circuit 530 may beinadequate because the probability that the noisy DQS signal will notstay within the hysteresis voltage range during certain indeterminateperiods is simply too high. For example, it is not uncommon for aringing (such as is illustrated in FIG. 6) to occur at a point in timeright after completion of the postamble (i.e. at the beginning of T5).As a result of such ringing, DQS can shoot up to a voltage relativelyclose to logic high, and perhaps above VR1 in a manner so as to causeanomalous behavior of the type aforementioned in this disclosure.

With respect to the illustrated example, it will be seen that thepreamble and postamble present in the input signal VI are missing in theoutput signal Q. It should be understood however that this is notcharacteristic of all examples of incorrupted strobe signals produced bycontemplated circuit embodiments having similarity to the DQS transitiondetection circuit 530. For example, generation of an output strobe thatincludes a preamble could be accomplished with the addition of only somerelatively non-complex circuitry to the DQS transition detection circuit530.

With reference again to FIG. 1, it should be noted that a single memorycontroller 20 and a single DDR SDRAM 22 have been shown for convenienceof illustration only, and it will be understood that example embodimentsare in no way limited to SDRAM devices that consist of only a singlecontroller providing commands to a single memory chip. In some examplesthe SDRAM device 10 will include a single memory controller 20 andmultiple DDR SDRAMs 22. In other examples the SDRAM device 10 willinclude multiple memory controllers 20 and multiple DDR SDRAMs 22.

Although example embodiments have been described with reference to DDRSDRAM, it will be understood that at least some example embodiments canbe employed in other memory devices that might not be categorized as DDRSDRAM. For example, at least some example embodiments can be employed inQuad Data Rate SDRAM (QDR SDRAM) and Extreme Data Rate SDRAM (XDRSDRAM).

Various circuits and circuit components described in the precedingdetailed description of example embodiments can be considered to be of atype performing known operations on electronic signals. Those skilled inthe art will have knowledge of alternative circuits or circuitcomponents which are recognized as equivalent because they provide thesame operations on the signals.

Certain adaptations and modifications of the described embodiments canbe made. Therefore, the above discussed embodiments are considered to beillustrative and not restrictive.

1. A method for preamble detection within a microelectronics system, themethod comprising: receiving a clock signal of the type in which aseries of regular pulses in voltage level of said clock signal arepreceded by a preamble period having a beginning and an end, atransition in said clock signal from an indeterminate logic level to aselected one of a high logic level and a low logic level occurring atsaid beginning of the preamble period; receiving a complement of saidclock signal, a transition in said complement of the clock signal fromsaid indeterminate logic level to the other of the logic levelsoccurring at said beginning of the preamble period; generatingindication that said beginning of the preamble period has occurred by:i) detecting said transition in the clock signal based on when thevoltage level of the clock signal crosses through a first threshold of avoltage range; and ii) detecting said transition in said complement ofthe clock signal based on when the voltage level of said complement ofthe clock signal crosses through a second threshold of said voltagerange.
 2. The method as claimed in claim 1, wherein said clock signal isa data strobe clock (DQS) signal and said complement of the clock signalis a complement of said DQS signal.
 3. The method as claimed in claim 2,wherein the selected one of the logic levels is said low logic level,and the other of the logic levels is said high logic level.
 4. Themethod as claimed in claim 1, wherein the detecting said transition inthe clock signal is carried out by a comparator having one of its inputsreceiving a reference voltage at said first threshold.
 5. The method asclaimed in claim 4, wherein said one of the inputs is an invertinginput, and said first threshold is higher than said second threshold. 6.The method as claimed in claim 1, wherein the detecting said transitionin said complement of the clock signal is carried out by a comparatorhaving one of its inputs receiving a reference voltage at secondthreshold.
 7. The method as claimed in claim 6, wherein said one of theinputs is an inverting input, and said first threshold is higher thansaid second threshold.